There is a technique for detecting the line of sight of a subject person based on a cornea reflection technique by using a near-infrared light source and a near-infrared camera (for example, see Takehiko Ohno et al., “An Eye Tracking System Based on Eye Ball Model—Toward Realization of Gaze Controlled Input Device”, Information Processing Society of Japan 2001-HI-93, 2001, pp. 47-54 (which will be referred to as “Non Patent Literature 1” hereinafter)). The cornea reflection technique involves generating reflection on the cornea by using a near-infrared light source and determining the center of the reflection and the center of a pupil in accordance with image processing. Then, in the cornea reflection technique, the line of sight of the subject person is detected based on the positional relationship between the center of the reflection and the center of the pupil. In the image processing for detecting the pupil, an image processing device detects an eye region and also detects pupil candidates from the eye region by using template information.
There is also a technique for calculating the brightness of the eye region and identifying a pupil candidate having a radius closest to the radius corresponding to the current brightness from among the previously-detected pupil candidates based on brightness pupil information prepared in advance (for example, see Japanese Laid-open Patent Publication No. 2013-215549 (which will be referred to as “Patent Literature 1” hereinafter)). Specifically, the image processing device identifies a real pupil from among the pupil candidates by using the brightness of the eye region in an image to be processed.